Econintersect: Two stories today (15 August 2012) in the daily e-mail from Scientific Computing address different interesting areas of extraterrestrial science: stars and things on earth that arrived from space. One of the stories describes the latest research on a cluster of four giant stars each of a size that has not yet been found elsewhere in the universe. The second story (about ‘star dust’) involves a research report that presents “convincing evidence” that a class of materials called “quasicrystals” that have been found only rarely in nature must have reached earth via transport in meteors.
Giant Star Cluster
The four largest stars ever discovered actually exceed the previously presumed limit for star masses (150 times the mass of our sun). The largest of the four in the so-called R-136 cluster is more than double the previously presumed size limit. Progressive close-ups of the cluster are shown in the following graphic.
Click on graphic for larger image.
The researchers did detailed multi-body modelling and have determined that these super sized stars are a natural consequence of having very large binary star couplings in close proximity. Collisions produce coalescence into the mega-stars.
From the paper:
Among the most remarkable features of the stellar population of R136, the central, young, massive star cluster in the 30 Doradus complex of the Large Magellanic Cloud, are the single stars whose masses substantially exceed the canonical stellar upper mass limit of 150 M_sun. A recent study by us, viz., that of Banerjee, Kroupa & Oh (2012; Paper I), which involves realistic N-body computations of star clusters mimicking R136, indicates that such “super-canonical” (SC) stars can be formed out of a dense stellar population with a canonical initial mass function (IMF) through dynamically induced mergers of the most massive binaries. Here we study the formation of SC stars in the R136 models of Paper I in detail. To avoid forming extraneous SC stars from initially highly eccentric primordial binaries as in Paper I, we compute additional models with only initially circular primordial binaries. We also take into account the mass-evolution of the SC stars using detailed stellar evolutionary models that incorporate updated treatments of stellar winds. We find that SC stars begin to form via dynamical mergers of massive binaries from approx. 1 Myr cluster age. We obtain SC stars with initial masses up to approx. 250 M_sun from these computations. Multiple SC stars are found to remain bound to the cluster simultaneously within a SC-lifetime. These properties of the dynamically formed SC stars are consistent with those observed in R136. In fact, the stellar evolutionary models of SC stars imply that had they formed primordially along with the rest of the R136 cluster, i.e., violating the canonical upper limit, they would have evolved below the canonical 150 M_sun limit by approx. 3 Myr, the likely age of R136, and would not have been observable as SC stars at the present time in R136. This strongly supports the dynamical formation scenario of the observed SC stars in R136.
Quasicrystals are a class of materials that contain multiple types of “normal” crystal structures that repeat in complex patterns throughout any sample of quasicrystalline materials. They were synthesized in the laboratory for the first time in 1982 by Dan Schechtman, professor of materials science at Israels’s Technion and also at Iowa State University. The 1982 discovery occurred while Schechtman was working while on a sabbatical at Johns Hopkins University in Baltimore. He received the Nobel Prize in Chemistry for that work in 2011. The class of materials has produced a number of widely used applications from non-stick culinary items to ball bearing with unique properties.
The abstract of the recent paper by Paul J. Steinhardt (princeton University) and Luca Bindi (Università di Firenze) on the discovery and analysis of quasicrystal samples from eastern Russia:
The concept of quasicrystals was first introduced twenty-eight years ago and, since then, over a hundred types have been discovered in the laboratory under precisely controlled physical conditions designed to avoid crystallization. Yet the original theory suggested that quasicrystals can potentially be as robust and stable as crystals, perhaps even forming naturally. These considerations motivated a decade-long search for a natural quasicrystal culminating in the discovery of icosahedrite (Al63Cu24Fe13), an icosahedral quasicrystal found in a rock sample composed mainly of khatyrkite (crystalline (Cu,Zn)Al2) labeled as coming from the Koryak Mountains of far eastern Russia. In this paper, we review the search and discovery, the analysis showing the sample to be of extraterrestrial origin and the initial results of an extraordinary geological expedition to the Koryak Mountains to seek further evidence.
Picture by Eric Weeks, Emory University Physics Dept., showing quasicrystal tiling with five-fold symmetry. Visit here to read of his research and see more interesting pictures of quasicrystal tiling.
- Astronomers Crack Monster Star Mystery (Scientific Computing, 15 August 2012)
- Convinving Evidence found for Extra-terrestial Origin of Quasicrystals (Scientific Computing, 15 August 2012)
- The emergence of super-canonical stars in R-136-type star-burst clusters (Sambaran Banjerjee, Pavel Kroupa and Seungkyung Oh (all University of Bonn), to be published MNRAS)
- In search of natural quasicrystals (Paul J. Steinhardt and Luca Bindi, Reports on Progress in Physics, Vol. 75 No. 9 2012)